This invention relates to a power transmission mechanism such as a clutch device for power transmission.
A one-way clutch device, for example, is used as a clutch device for performing power transmission switching.
The one-way clutch device is characterized in that a rotational force is transmitted only in one direction, i.e. only from a driving-shaft side to a driven-shaft side, but not from the driven-shaft side to the driving-shaft side.
The one-way clutch device is applied to, for example, a film feeder mechanism for use in a camera as disclosed in Japanese Patent Application KOKAI Publication No. 3-200128.
FIG. 12 shows a driving force transmission system incorporated in the film feeder mechanism.
In the film feeder mechanism, the driving force of a driving motor 103 as a driving source is transmitted to a sun gear 106, incorporated in a planetary gear mechanism, via a pinion 104 and a gear train 105. A planetary gear 107 incorporated in the planetary gear mechanism is selectively engaged with a driven gear 108 or a driven gear 109. The driven gear 108 is coupled to a gear 102a attached to a spool shaft 102 via a spool-side gear train 111, and also to an input-side gear 110a incorporated in a one-way clutch 110.
On the other hand, the driven gear 109 is engaged with an output-side gear 110b incorporated in the one-way clutch 110. The output-side gear 110b is coupled to a cartridge driving gear 113 via a cartridge-side gear 112.
The cartridge driving gear 113 has a fork section 113a engaged with a cartridge shaft 114. Concerning the one-way clutch 110, a direction indicated by arrow D13 is supposed to be the forward direction of rotation.
When forwarding a film 120b y the film feeder mechanism, the driven gear 108 is rotated via the planetary gear mechanism in a direction indicated by arrow D11. The cartridge driving gear 113 rotates via the one-way clutch 110 and the gear train 112 to forward the film 120. At the same time, the spool shaft 102 is also driven via the spool shaft gear train 111. When winding the forwarded film 120 on the spool shaft 102, the spool-shaft side forwarding speed is set higher than the cartridge-side speed.
Accordingly, an over-running state occurs in which the cartridge driving shaft 113 rotates at a high speed, and the output-side gear 110b is driven in the direction D13 at a relatively higher speed than the input-side gear 110a. The winding operation when photographing is the same as the above driving operation.
When rewinding the film, the motor 103 is rotated in an opposite direction to the above to engage the planetary gear 107 with the driven gear 109, whereby the driven gear 109 is rotated via the planetary gear mechanism in a direction indicated by arrow D12. Then, the output gear 110b of the one-way clutch 110 is directly rotated in a direction opposite to the direction D13, thereby rewinding the film 120 on the cartridge shaft. At this time, the spool shaft 102 is rotated in a direction opposite to the direction indicated by the arrow, in accordance with the movement of the film 120.
FIG. 13A illustrates an example of a structure of the one-way clutch.
In FIG. 13A, a driven-side ring 201 is constructed such that it covers a driving-side input shaft 202 with a predetermined space interposed therebetween. In this example, two rollers 200a and 200b are movably provided in the spaces defined between the driven-side ring 201 and the input shaft 202. When the driving-side input shaft 202 rotates in a direction indicated by arrow A, the rollers 200a and 200b each contact both an inner surface 201a of the driven-side ring 201 and a flat surface 202a of a cam section 202b of the driving-side input shaft 202. As a result, the driving force of the driving-side input shaft 202 is transmitted to the driven-side ring 201 via the rollers 200a and 200b, which means that both the input shaft 202 and the driven ring 201 rotate in the direction A. After the driving-side input shaft 201 starts to rotate at a higher speed than the ring 202, the rollers 200a and 200b are pushed by the inner surfaces 201a of the driven-side ring 201 in the direction of the rotation of the ring 201, thereby releasing the rollers held between the inner surfaces 201a and the flat surfaces 202a, and hence stopping the transmission of the driving force from the driving-side input shaft 202 to the driven-side ring 201.
When the rotational speed of the driving-side input shaft 202 has again become relatively higher than the driven-side ring 201, the two rollers 200a and 200b are held between the input shaft 202 and the ring 201 to thereby restart the transmission of the driving force from the input shaft 202 to the ring 201. On the other hand, when the driving-side input shaft 202 rotates in a direction indicated by arrow B, the rollers 200a and 200b are urged by the flat surfaces 202c of the input shaft 202, which does not cause the rollers 200a and 200b to be held between the input shaft 202 and the ring 201. As a result, no driving force is transmitted to the driven-side ring 201.
FIG. 13B is a sectional view of the one-way clutch.
As is shown in FIG. 13B, the driven-side ring 201 and the driving-side input shaft 202 are held between two bottom boards 203 and 204 such that the rollers 200a and 200b can move between the ring 201 and the input shaft 202.
As described above, the film feeder mechanism disclosed in Japanese Patent Application KOKAI Publication No. 3-200128 employs the one-way clutch 110 for linking the spool shaft with the cartridge side. However, the one-way clutch 110 cannot cause two-way transmission of a force supplied from the input driving side, and hence it is necessary to directly drive the output-side gear 110b when rewinding the film 120a s shown in FIG. 12.
To directly drive the output-side gear 110b, it is necessary to use another driving system for directly driving the gear 110b. Further, since the one-way clutch 110 has to be located between the cartridge driving system and the spool driving system, much space is required in the camera, and the structure of the camera is inevitably complicated.